The Origin of the Meta-Anorthositic Gabbros and Garnetiferous Granulites of the Sittampundi Complex, Madras, India
The Origin of the Meta-Anorthositic Gabbros and Garnetiferous Granulites of the Sittampundi Complex, Madras, India
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发表时间：
1975-12
影响因子：
1.3
通讯作者：
A. Janardhanan;B. Leake
中科院分区：
文献类型：
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作者：
A. Janardhanan;B. Leake
本文对21个变质斜长角闪岩辉长岩、9个镁铁质岩（主要为石榴麻粒岩）和15个围岩及捕虏体的主量元素和微量元素进行了新的化学分析，讨论了该高度变质杂岩的岩石化学特征。该杂岩的火成成因得到证实，这与一些早期的观点相反，即富含钙长石的岩石是变质沉积钙硅酸盐成因的。麻粒岩和变斜长岩给出一致的，因此同源的火成岩的变化趋势，这表明他们从一个岩浆结晶的镁铁质和长英质部分分离变量晶体沉降。变质岩浆围岩，特别是角闪岩，不是同一套岩石的一部分。“正常化”的关键微量元素含量（如铬，镍，锶）的重要性，以恒定的镁铁质或长英质矿物的百分比，以允许广泛不同的丰度从富长英质和富镁铁质岩石的证明。该程序允许火成岩的变化趋势进行更严格的评价，并在目前的岩石，导致建议，一些铬在变斜长岩最初是作为铬铁矿，一个观点，根据发生富铬铁矿层的侵入。变质斜长岩中的角闪石不含辉石，从结构和角闪石成分来看，其结晶是变质的。它究竟是重结晶的原生火成角闪石，还是由辉石、橄榄石和斜长石变质作用形成的，尚不能确定。一些化学标准，可能使原生火成角闪岩的结晶，甚至当变质重结晶，被认可的建议，虽然他们的应用程序，目前的入侵并没有导致一个明确的结论，他们可能是有用的其他地方。
The petrochemistry of the highly metamorphosed complex is discussed using new chemical analyses for major and trace elements of 21 meta-anorthositic hornblende gabbros, 9 mafic rocks, mostly garnetiferous granulites, and 15 country rocks and xenoliths. The igneous origin of the complex is confirmed, contrary to some earlier views that the anorthite-rich rocks were of metasedimentary calc-silicate origin. The granulites and meta-anorthositic rocks give congruent, and therefore consanguineous igneous trends of variation, suggesting that they crystallized from one magma being the mafic and felsic portions separated by variable crystal settling. The metamagmatic country rocks, especially the amphibolites, are not part of the same suite. The importance of 'normalising' critical trace element contents (e.g, Cr, Ni, Sr) to constant mafic or felsic mineral percentage to allow for the widely differing abundances obtained from felsic-rich and mafic-rich rocks is demonstrated. The procedure allows igneous trends of variation to be much more critically appraised, and, in the present rocks, leads to the suggestion that some of the Cr in the meta-anorthositic rocks was originally present as chromite, a view in accordance with the occurrence of chromite-rich layers in the intrusion. The hornblende in the meta-anorthositic rocks, which are pyroxene-free, is metamorphic in crystallization from the texture and the hornblende composition. Whether it is recrystallized primary igneous hornblende or was derived by metamorphism of pyroxene, olivine and plagioclase is uncertain. Some chemical criteria that might enable the crystallization of primary igneous hornblende, even when metamorphically recrystallized, to be recognised are suggested and although their application to the present intrusion does not lead to an unequivocal conclusion, they may be useful elsewhere.